Platelets are anucleate fragments of megakaryocyte cytoplasm. They are pivotal for haemostatic plug formation, both by forming the initial thrombus at the site of vascular lesion and by providing template for coagulation protein assembly with subsequent thrombin generation resulting in conversion of fibrinogen to fibrin which interacts with the activated platelets through the GPIIb/IIIa receptor forming the haemostatic clot [Roberts et al. 2006] and by maintaining vascular wall integrity [Nachman and Rafii 2008]
Under physiologic conditions, platelet aggregation and haemostasis is prevented by the vascular endothelium. The endothelium provides a physical barrier and secretes platelet inhibitory products, such as prostacycline (PGI2) and nitric oxide (NO). These compounds regulate the adhesiveness of platelets and the activation state of the platelet receptor GPIIb/IIIa in a paracrine way and also maintain the endothelium in a quiescent state through autocrine mechanisms [Zardi et al 2005].
With endothelial activation or injury (trauma, critical illness like sepsis, atherosclerosis), platelets adhere to the endothelium or subendothelium, respectively. This adhesion activates platelets, causes a shape change and a release reaction where ADP is released (which is a potent platelet agonist). The platelet membrane integrin receptor, GPIIb/IIIa, becomes activated. Fibrinogen binds to this receptor, effectively cross-linking platelets to form a platelet plug. During platelet activation, thromboxane A2 is formed from hydrolysis of phospholipids (especially phosphatidylcholine) in the platelet membrane. This is an important platelet agonist, recruiting other platelets and activating them, thus promoting further platelet aggregation. Thrombus formation is a problem in many clinical situations, mainly cardiovascular diseases where platelets are also involved in atherothrombotic disease where they support development of thrombus formation on atherosclerotic plaques eventually resulting in occlusion of vessels and cell death, exemplified by acute myocardial infarction [De Meyer et al. 2009].
In Intensive Care Unit (ICU) patients and especially in sepsis, pathologic thrombus formation attributed to inflammation induced endothelial dysfunction and platelet activation is likely to be one of the main causes of morbidity and mortality. Thus, almost half of all patients with sepsis, major trauma or other critical illness present with or develop thrombocytopenia. In critically ill patients, thrombocytopenia upon arrival to the intensive care unit (ICU), is common and is associated with increased mortality [Moreau et al. 2009], longer ICU stays, a higher incidence of bleeding events, greater transfusion requirements and regardless of the cause, thrombocytopenia or declining platelet count is an independent predictor of multi organ failure (MOF) [Nguyen and Carcillo 2006] and ICU mortality [Levi and Lowenberg 2008]. The pathogenesis of low or declining platelet count in critically ill patients is multifactorial and involve e.g., bleeding, sepsis, thrombotic microangiopathy including disseminated intravascular coagulation (DIC) and immune or drug-induced thrombocytopenia [Nguyen and Carcillo 2006; Levi and Lowenberg 2008].
Thrombocytopenia and a decline in platelet count may reflect the same pathophysiologic disturbances seen in sepsis, disseminated intravascular coagulation (DIC), vitamin deficiencies, macrophage activation, drug-induced toxicity, liver disease, haematologic disorders, massive transfusions, immune mediated thrombocytopenia and unidentified factors ref [Moreau et al. 2007]. The increased mortality in critically patients with thrombocytopenia is complex and relates also in part to development of progressive organ failure accompanied by a decline in platelet count, thrombocytopenia associated multi organ failure (TAMOF). TAMOF is a thrombotic microangiopathic syndrome that can be defined by a spectrum of pathology that includes disseminated intravascular coagulation (DIC) and secondary thrombotic microangiopathy (TMA) [Nguyen and Carcillo 2006].
A common feature for TAMOF is the progressive decline in platelet count related to systemic profound coagulation activation, down-regulation of both fibrinolysis and natural anticoagulants resulting in platelet consumption and microvascular thrombus formation where the platelets play an integral role [Nguyen and Carcillo. 2006]. A non-exhaustive list of conditions associated with TAMOF is presented in Table 1.
TABLE 1Conditions associated with organfailure, including MOF and TAMOFCancerTransplantation (solid organs, haematopoietic stem cells)Cardiovascular surgery/cardiopulmonary bypass/extracorporealmembrane oxygenation (ECMO)Vascular surgeryAutoimmune diseaseSystemic infectionVasculitisExposure to toxinsCyclosporine A therapyFK 506 therapyChemotherapyRadiationTiclopidine treatmentHemolytic Uremic Syndrome variant syndromes.Trauma (e.g. polytrauma, neurotrauma, fat embolism)
Non-exhaustive list of conditions associated with TAMOF-DIC is presented in Table 2.
TABLE 2Clinical conditions that may be associatedwith disseminated intravascular coagulationSepsis/severe infection (any microorganism)MalignancyMyeloproliferative/lymphoproliferative malignanciesSolid tumorsMetastasisTrauma (e.g. blunt/penetrating trauma, polytrauma, neurotrauma, fatembolism, burn trauma)Obstetrical calamitiesAmniotic fluid embolismAbruptio placentaeOrgan destruction (e.g. severe pancreatitis)Severe toxic or immunologic reactionsSnake bitesRecreational drugsTransfusion reactionsTransplant rejection (graft vs. host disease, host vs. graft disease)Vascular abnormalitiesKasabach-Merritt syndromeLarge vascular aneuysmsSevere hepatic failureEmbolismThromboembolismCholesterol embolismFat embolismAir embolismSeptic embolismTissue embolismForeign body embolismAmniotic fluid embolism
Standard treatment in the intensive care unit of critically ill patients with or without thrombocytopenia focuses on:
1. Identification and specific treatment of the underlying disorder causing the patients condition, and
2. support of vital organs in case of failure exemplified by ventilatory support, haemodialysis, vasopressor treatment, parenteral nutrition, fluid support, corticosteroids, tight glycemic control, administration of blood products and others generally referred to as intensive care management [Bick R. 1996, Bick R. 1998].
Furthermore, the treatment may include attenuation of the procoagulant condition by systemic administration of agents which decrease enzymatic coagulation activation such as:
1. Heparins (low molecular weight heparin (LMWH), unfractioned heparin (UFH))
2. Thrombin inhibitors
3. Antithrombin
4. Tissue factor pathway inhibitor (TFPI)
5. Activated Protein C
have been evaluated and especially in critically ill patients with severe sepsis which carries a high mortality (>50%).
Ad 1. Heparins
Meta-analysis suggests that venous thromboembolism (VTE) prophylaxis with an LMWH (including fondaparinux) or UFH is effective in reducing the rate of deep venous thrombosis (DVT), but this benefit did not extend to enhanced protection against pulmonary embolism (PE). Additionally, LMWH and UFH had similar bleeding outcomes and hence VTE prophylaxis with heparins is standard therapy in critically ill medical and surgical patients, also in the ICU. It is recommended that, on admission to the ICU, all patients are assessed for their risk of VTE, and that most receive thromboprophylaxis (Grade 1A) [Kanaan et al. 2007, Geerts et al. 2008].
Ad 2. Thrombin Inhibitors
Direct thrombin inhibitors (DTIs) act as anticoagulants (delaying blood clotting) by directly inhibiting the enzyme thrombin. There are two types of DTIs, dependent on their interaction with the thrombin molecule. Bivalent DTIs (hirudin and analogs) bind both to the active site and exosite 1, while univalent DTIs bind only to the active site. Bivalent: Hirudin, Bivalirudin, Lepirudin, Desirudin; Univalent: Argatroban, Melagatran, Dabigratan
Ad 3. Antithrombin
A Cochrane analysis included 20 randomized trials with a total of 3458 participants; 13 of these trials had high risk of bias. When combining all trials, AT III did not statistically significantly reduce overall mortality compared with the control group (RR 0.96, 95% CI 0.89 to 1.03; no heterogeneity between trials). A total of 32 subgroup and sensitivity analyses were carried out. Analyses based on risk of bias, different populations, and the role of adjuvant heparin gave insignificant differences. AT III reduced the multiorgan failure score among survivors in an analysis involving very few patients. AT III increased bleeding events (RR 1.52, 95% CI 1.30 to 1.78). ATIII therapy of critically ill patients is not recommended [Afshari et al. 2008].
Ad 4. TFPI
Efficacy and safety of tifacogin (recombinant tissue factor pathway inhibitor) in severe sepsis was evaluated in a randomized controlled trial (OPTIMIST) encompassing 1754 patients. All cause mortality in the TFPI treated group was 34.2% vs 33.9% in placebo treated patients, p=0.88. Tifacogin administration was associated with an increase in risk of bleeding, irrespective of baseline INR and there is currently no indication for TFPI treatment of patients with severe sepsis [Abraham et al. 2003].
Ad 5. Activated Protein C
The PROWESS study in patients with severe sepsis was prematurely stopped at the second interim analysis because of a significant reduction in mortality in the APC treated patients [Bernard et al 2001]. A total number of 1728 patients were included and randomized in this study, of which 1690 were eligible for analysis. Of these patients, 840 were randomized to receive recombinant human APC at a dose of 24 mg/kg/h for 96 h, and 850 patients received placebo. Mortality was 24.7% in the APC group as compared with 30.8% in the placebo group (relative risk reduction 19.4 percentages, 95% confidence interval 6.6-30.5). The series of negative trials in specific populations of patients with severe sepsis performed after the PROWESS study has added to the scepticism regarding the use of APC [Marti-Carvajal et al. 2007]. Furthermore, on the basis of the ADDRESS study, treatment with APC seems not to be indicated in patients with sepsis and a relatively low disease severity [Levi M 2008]. No consensus regarding the use of APC in patients with severe sepsis exists today.
Despite all these initiatives, many patients do not achieve homeostasis, continue to bleed, become immunodeficient, loose endothelial wall integrity (the endothelial wall becomes activated), and/or develop MOF and/or TAMOF and die. Thus, there remains a need for a method of treatment for critically ill patients; a method which may include treatment and/or prevention of development of organ failure such as MOF and/or TAMOF, and/or arrest bleeding, and/or prevent immunodeficiency, and/or preserving endothelial integrity in critically/acutely ill patients and furthermore, there is a need for a composition that may be used in this method.